The present invention relates to a process for detoxifying waste or decontaminating liquid effluents and/or waste gases. More particularly, the present invention relates to such a process for example wherein the liquid effluent or waste water contains chromium (VI) compounds and/or the waste or flue gases, effluents or acid rinsing waters contain NO and/or NO.sub.2. The NO and/or NO.sub.2 component will in the following be referred to as NO.sub.x wherein x may represent numerical values between 0,5 and 2 and NO.sub.2 is identical with N.sub.2 O.sub.4.
The process of the invention may be applied in the purification and/or detoxification of effluents or flue gases containing NO and/or NO.sub.2 and chromium (VI)-containing waste waters or solutions.
In many electrochemical processes in which electrolytes containing chromium salts are used, effluents are produced which contain chromium (VI), the removal of which for environmental reasons is required because of the high toxicity of chromium (VI) compounds. Such removal is, however, problematic and costly. These poisonous effluents may contain hexavalent chromium in the form of CrO.sub.4.sup.2- anions or Cr.sub.2 O.sub.7.sup.2- anions depending on the pH value. Because chromium (VI) compounds are many times as poisonous as chromium (III) compounds, or because chromium (III) compounds compared with chromium (VI) compounds are virtually not toxic, most detoxification methods for chromium (VI)-containing effluents carried out at present on a technical scale rely on a reduction of the chromium (VI) to chromium (III) compounds.
At present, detoxification of such effluents containing chromium (VI) is carried out with the aid of commercially available chemicals of specified composition having a strong reducing action. Iron (II) sulphate or alkali sulphites in particular are commonly used as such commercially available chemicals. These chemicals suffer the disadvantage that they are expensive, that they are usually not available in the same plant and accordingly are subject to additional freight and transportation costs and involve substantial manipulation costs. In addition, the reaction products of those chemicals contaminate the effluent.
It is an object of the present invention to avoid either fully or at least partly the use of such commercially available chemicals.
It is also an object of the present invention to utilise in the same industrial plant where possible, two groups of polluting substances to render both groups effectively harmless.